1. Field of the Invention
This invention relates to power plant systems having elastic fluid turbines, and more particularly, to means for increasing the power plant's cycle efficiency using a dry cooling scheme.
2. Description of the Prior Art
Cycle efficiency of power plant systems increases when zoned or multi-pressure condensers are used. Such use is most feasible on elastic fluid turbines having multiple exhaust ports. When it is desired to pass elastic cycle fluid on the shell side of a condenser, zoning may consist of physically separating the condenser shells or dividing one shell by including appropriate divisional walls. When it is desired to pass elastic cycle fluid through heat exchange conduits, physical division of the shell is unnecessary since zoning results from segregating the cycle fluid exiting from each turbine exhaust port in a separate conduit or set of conduits.
Cooling the condensing zones in divided or separated shells has often been accomplished by circulating water or other coolant through conduits extending through those zones. The selected coolants typically increased in temperature, but remained in the liquid phase while traversing the coolant conduits. The conduits usually linked the condensing zones in series flow relation since series flow coolant schemes required lower coolant flow rates than did parallel coolant flow schemes when both utilized constant phase coolant therein such as water. Condenser shell separation zoning or cycle fluid segregation, while increasing cycle efficiency, adds complexity and cost and becomes economically advantageous when the condenser coolant's temperature rise becomes high. Temperature rises characteristically increase from once-through cooling to wet cooling to dry cooling with the relatively large temperature rises being typical of dry cooling.
While dry cooling requires higher capital costs than wet cooling and wet cooling, in turn, has higher capital costs than once-through cooling, it is often desirable to obtain dry cooling's advantages of substantially no makeup coolant being required in the condenser cooling circuit, vapor plumes from the cooling towers being eliminated, and environmental coolant temperature rise restrictions for once-through systems being overcome. In addition to dry cooling's greater hardware costs than both wet cooling and once-through cooling, dry cooling often suffers from greater operating costs. The relatively greater operating costs are primarily due to optimization of heat transfer area and operating cost. To maintain the capital cost of heat transfer surface area at an acceptable level it is often necessary to reduce the cycle efficiency by either consuming more power in forced convection or allowing higher condensing temperatures. Additionally, dry cooling, as well as wet cooling, consumes large quantities of pumping power used to circulate liquid coolant such as water which has absorbed sensible heat from the cycle elastic fluid vapor and must then, itself, be cooled.
The previously mentioned disadvantages of dry cooling could be greatly minimized by lowering the cycle vapor's condensing temperature and pressure, decreasing the heat transfer surface area required by previous dry cooling schemes, and reducing the pumping power required by both wet and dry cooling systems.